The present invention relates to a group-III nitride semiconductor light-emitting device comprising a substrate such as silicon (Si) having on the surface thereof a light-emitting part structure containing a gallium nitride phosphide (GaN1xe2x88x92XPX, wherein 0 less than X less than 1) single crystal layer provided via a boron phosphide (BP)-based buffer layer.
A group-III nitride semiconductor light-emitting device that emits light in the blue or green band is composed of a multilayer structure where a gallium nitride (GaN) crystal layer as one constituent element is disposed, for example, on a sapphire (xcex1-Al2O3) single crystal substrate using a growing technique, such as metal organic chemical vapor deposition (MOCVD) method. The multilayer structure has a light-emitting part structure undertaking the function of emitting light. Conventionally, the light-emitting part structure in general takes a pn junction-type hetero structure constructed by a p-type or n-type clad layer consisting of a light-emitting layer formed of gallium indium nitride (GayIn1-YN, wherein 0 less than Yxe2x89xa61) and an aluminum gallium indium nitride (AlGaInN)-based crystal layer.
FIG. 5 is a schematic sectional view showing an example of the construction of a conventional multilayer structure light-emitting device (LED) 100 having a pn junction-type double hetero (DH) junction light-emitting part structure 42 comprising an AlGaInN-base crystal layer. In a conventional multilayer structure, the light-emitting part structure 42 is composed of, for example, a lower clad layer 103 comprising an n-type aluminum gallium nitride (AlZGa1xe2x88x92ZN, wherein 0xe2x89xa6Zxe2x89xa61) crystal layer, a light-emitting layer 104 comprising an n-type gallium indium nitride (GaYIn1-YN) and an upper clad layer 105 comprising a p-type aluminum gallium nitride (AlZGa1xe2x88x92ZN, wherein 0xe2x89xa6Zxe2x89xa61) (see, JP-A-6-260682 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)). The functional layers 103 to 105 constituting the light-emitting part structure 42 each is usually deposited with an intervention of a buffer layer formed at a temperature lower than the temperature at the formation of those functional layers, so-called a low-temperature buffer layer 102 (see, JP-A-4-297023). Furthermore, in a multilayer structure comprising a sapphire substrate 101 having provided thereon a group-III nitride semiconductor crystal layer, the low-temperature buffer layer 102 is usually composed of aluminum gallium nitride (AlZGa1xe2x88x92ZN, wherein 0xe2x89xa6Zxe2x89xa61) (see, JP-A-6-151962).
The low-temperature buffer layer 102 is provided mainly for the purpose of reducing the lattice mismatch between the sapphire substrate 101 and the lower clad layer 103 composed of AlZGa1xe2x88x92ZN crystal, thereby obtaining a good group-III nitride single crystal layer reduced in the density of crystal defects such as dislocation. Particularly, in a known conventional example, the low-temperature buffer layer 102 is composed of gallium nitride (GaN), the lower clad layer 103 is composed of a GaN layer formed at a high temperature in excess of the temperature for the formation of the low-temperature buffer layer 102, and the light-emitting layer 104 is composed of a gallium indium nitride mixed crystal phase (see, JP-A-6-216409).
Furthermore, in the conventional light-emitting device shown in FIG. 5, the substrate 101 is an insulating sapphire and therefore, a part of the lower clad layer 103 must be removed to provide an n-type ohmic electrode 107. A p-type ohmic electrode 106 is provided on the electrically conducting upper clad layer 105.
However, the mismatch between the sapphire substrate and the GaN layer constituting the low-temperature buffer layer is as high as about 13.8% (see, Nippon Kessho Seicho Gakkai Shi (Journal of Japan Crystal Growth Society), Vol. 15, Nos. 3 and 4, pp. 74-82 (Jan. 25, 1989)) and therefore, a continuous low-temperature buffer layer cannot be stably obtained at present. In the discontinuous portion partially present in the low-temperature buffer layer due to the lacking of film continuity, namely, in the region where the sapphire substrate surface is exposed, hexagonal GaN predominantly grows in the c-axis direction thereof. As a result, dislocation is generated starting from the coalescence of GaN columnar crystals, propagates to the GaInN light-emitting layer via the upper GaN layer and disadvantageously deteriorates the crystal quality of the light-emitting layer. In other words, according to the above-described conventional multilayer structure constructed by stacking a GaInN light-emitting layer on a GaN low-temperature buffer layer via a GaN layer, a good GaInN-type light-emitting layer film cannot be formed due to the propagation of crystal defects such as dislocation attributable to the discontinuity of the low-temperature buffer layer. Therefore, stable formation of a light-emitting part structure comprising a group-III nitride single crystal layer having excellent operation reliability or ensuring long device life cannot be attained particularly in the case of a laser diode (LD).
The present invention has been made by taking into account these problems in conventional techniques, and an object of the present invention is to provide a buffer layer having continuity capable of allowing homogeneous coating on the substrate surface and preventing generation of dislocations despite a large mismatch with the substrate crystal. Another object of the present invention includes providing a construction of a group-III nitride single crystal layer structure deposited on the above-described buffer layer, which is reduced in the density of crystal defects such as dislocation and favored with excellent crystallinity.
More specifically, the group-III nitride semiconductor light-emitting device of the present invention is a group-III nitride semiconductor light-emitting device comprising a single crystal substrate having thereon a light-emitting part structure containing a gallium nitride phosphide (GaN1xe2x88x92XPX, wherein 0 less than X less than 1) single crystal layer provided via a boron phosphide (BP)-based buffer layer.
By using the boron phosphide-based buffer layer, the lattice mismatch of crystals between the substrate and the gallium nitride phosphide light-emitting part structure can be eliminated and a gallium nitride phosphide light-emitting part structure having excellent crystallinity can be formed. As a result, a high-emission intensity light-emitting device can be advantageously obtained.
In the group-III nitride semiconductor light-emitting device of the present invention, the boron phosphide-based buffer layer is amorphous.
The BP-based buffer layer is rendered amorphous by growing it at a low temperature, which has an effect of allowing the buffer layer to cope with a substrate having a lattice constant over a wide range.
In the group-III nitride semiconductor light-emitting device of the present invention, the BP-based buffer layer may be composed of an amorphous and crystalline multilayer structure.
By providing an amorphous BP-based buffer layer in the vicinity of an interface with the substrate and providing a crystalline BP-based buffer layer in the vicinity of the light-emitting part structure thereon, a gallium nitride phosphide light-emitting part structure having higher crystallinity can be advantageously obtained with ease.
In the group-III nitride semiconductor light-emitting device of the present invention, the light-emitting part structure may be a single hetero-junction structure containing a gallium nitride phosphide single crystal layer.
The light-emitting part can have good crystallinity and therefore, a high-emission intensity light-emitting device can be obtained even with a simple light-emitting part structure.
In the group-III nitride semiconductor light-emitting device of the present invention, the light-emitting part structure may be a double hetero-junction structure containing a gallium nitride phosphide single crystal layer.
By using a double hetero-junction structure, a light-emitting device having higher luminous intensity can be advantageously obtained.
In the group-III nitride semiconductor light-emitting device of the present invention, the degree of lattice mismatch between the BP-based buffer layer and the gallium nitride phosphide single crystal layer is preferably xc2x11% or less.
The degree of lattice mismatch between the BP-based buffer layer and the gallium nitride phosphide single crystal layer is more preferably xc2x10.4% or less.
This is because the lattice constant of boron phosphide-based buffer layer and the lattice constant of gallium nitride phosphide-based light-emitting layer can be approximated as close as possible by controlling the phosphorus composition. As the lattice mismatch is smaller, a good epitaxial crystal layer reduced in crystal defects can be more readily obtained, thereby contributing to the high-luminous intensity emission of the light-emitting device.
In the group-III nitride semiconductor light-emitting device of the present invention, the boron phosphide-based buffer layer is preferably composed of boron phosphide (BP) and in the light-emitting part structure, the gallium nitride phosphide single crystal layer preferably has a phosphorus (P) compositional ratio of 1 to 5%.
This is because the degree of lattice mismatch between the buffer layer and the light-emitting part is reduced to 1% or less, and as a result, a high-luminous intensity light-emitting device can be obtained.
Also, the present invention provides a lamp using the above-described group-III nitride semiconductor light-emitting device.
Furthermore, the present invention provides a light source using the above-described lamp.
The lamp using the group-III nitride semiconductor light-emitting device of the present invention and the light source using the lamp of the present invention each uses a high emission intensity light-emitting device and therefore, ensures brightness and excellent visibility.
The production method of a group-III nitride semiconductor light-emitting device of the present invention comprises a step of forming a boron phosphide (BP)-based buffer layer on a single crystal substrate and a step of providing a light-emitting part structure containing a gallium nitride phosphide (GaN1xe2x88x92xPx, wherein 0 less than X less than 1) single crystal layer.
By forming a boron phosphide (BP)-based buffer layer on a single crystal substrate and providing a light-emitting part structure containing a gallium nitride phosphide single crystal layer on the boron phosphide-based buffer layer, the lattice mismatch of crystal between the substrate and the gallium nitride phosphide crystal layer is relaxed, thereby forming a light-emitting part structure comprising gallium nitride phosphide crystal with excellent crystallinity.
The boron phosphide-based buffer layer is preferably amorphous. The buffer layer mainly composed of an amorphous has an effect of efficiently relaxing the lattice mismatch between the substrate and the gallium nitride phosphide single crystal layer or the like on the buffer layer.
Alternatively, the boron phosphide-based buffer layer preferably comprises an amorphous and crystalline multilayer structure. When an amorphous boron phosphide-based buffer layer is provided in a vicinity of the interface between the buffer layer and the substrate, and a crystalline boron phosphide-based buffer layer is provided in a vicinity between the buffer layer and the light-emitting part structure thereon, the obtained light-emitting part structure containing gallium nitride phosphide single crystal can readily have good crystallinity.
In the production method of a group-III nitride semiconductor light-emitting device of the present invention, the composition of the boron phosphide-based buffer layer or the gallium nitride phosphide single crystal layer is preferably controlled so that the degree of lattice mismatch between the boron phosphide-based buffer layer and the gallium nitride phosphide single crystal layer is xc2x11% or less, preferably xc2x10.4% or less. As the degree of lattice mismatch with the boron phosphide-based material constituting the buffer layer is smaller, the gallium nitride phosphide single crystal layer which becomes a light-emitting layer can have higher quality, whereby a high emission intensity semiconductor light-emitting device can be produced.
Furthermore, in the production method of a group-III nitride semiconductor light-emitting device of the present invention, the boron phosphide-based buffer is preferably composed of boron phosphide and the gallium nitride phosphide single crystal layer in the light-emitting part structure preferably has a phosphorus (P) compositional ratio of 1 to 5%. The boron phosphide is a binary compound and can be readily formed into a film by vapor phase growth means such as MOCVD method. When the phosphorus compositional ratio (X) of the gallium nitride phosphide (GaN1xe2x88x92xPx, wherein 0 less than X less than 1) single crystal layer is limited to the range from 1 to 5%, the degree of lattice mismatch with the boron phosphide constituting the buffer layer can be suppressed within about 0.4%, so that the formed Gan1xe2x88x92xPx single crystal layer can have reduced the density of crystal defects such as dislocation and excellent crystallinity. As a result, a light-emitting layer having excellent crystallinity can be obtained and a high emission intensity semiconductor light-emitting device can be produced.